Vacuum method and apparatus



H. S. CRANDALL VACUUM METHOD AND APPARATUS 2 Sheets-Sheet 1 INVEN TOR.

HARRY 5 GRAND/ILL BUCKHOR/V, BLORE, KLAROU/S 7' 8 SPAR/(MAN ATTORNEYS June 7, 1966 Filed March 12, 1963 June 1966 H. s. CRANDALL VACUUM METHOD AND APPARATUS 2 Sheets-Sheet 2 Filed March 12, 1963 HARRY S GRAND/ILL BUCKHORM BLORE, KLAROU/S 7' 8 SPAR/(MAN A 7' TORA/EYS United States Patent 3,254,783 VACUUM METHOD AND APPARATUS Harry S. Crandall, Portland, Oreg., assignor to Hyster Company, Portland, 0reg., a corporation of Nevada Filed Mar. 12, 1963, Ser. No. 264,627 11 Claims. (Cl. 214-650) This invention relates to improvements invacuum type load handling equipment, and particularly to improvements in the internal combustion engine of a load lifting vehicle of the type having suction pick up means, wherein the engine powers the vehicle from place to place and also serves as a source of vacuum for the suction pick up means. The invention also relates to a method of preventing the oversupply of fuel to the engine during vacuumizing periods.

It has been noted with engines of the above type that there is an oversupply of fuel during vacuumizing periods. This not only produces obnoxious fumes, but also decreases the power output of the engine and thus decreases the power output of the engine and thus decreases the power available for operating the vehicle, such as used in creeping up to a load, and for operating the main hoist ram and other power accessories. More importantly, this decrease in power output decreases the capacity of the engine as a vacuum pump and limits the extent of the vacuum that can be drawn. In addition, there is a chance that the engine will stall under such circumstances, thus interfering with load pick up operations.

A main object of the present invention is to provide a load lift vehicle of the above type so constructed that excess fuel is not supplied during vacuumizing periods, and to provide a vehicle in which substantially optimum airfuel ratio is achieved during both vacuumizing and ordinary periods of operation.

Another object is to provide in a vehicle of the type under consideration, a method of avoiding oversupply of fuel during vacuumizing periods, and to provide substantially optimum air-fuel ratio during .vacuumizing and ordinary periods of operation.

Another object of the invention is to provide a vehicle as described in the above object, in which means are provided to prevent boiling of the fuel during high temperature-low pressure operations.

An important object of the invention is to disclose how a standard commercial carburetor can be modified in a simple manner so that it can function to deliver a combustible mixture, of substantially optimum fuel-to-air ratio, to an engine when the engine is operating at normal intake air pressures and also at low intake air pressures.

Anotherobject is to provide such a carburetor properly for sustained periods of time at both normal and low intake air pressures, yet which has fast transitional re sponse to accurately track changes in intake air pressure.

A further object is to provide a carburetor and a carburetor system for an internal combustion engine which is used as a vacuum pump. I

Various other objects of the invention will be apparent from the following description taken in connection with the accompanying drawings wherein:

FIG. 1 is a somewhat diagrammatic view of a standard carburetor used with a lift truck engine;

FIG. 2 is a somewhat diagrammatic view in section through a vacuum pick up system embodying the concepts of the present invention;

FIG. 3 is a somewhat diagrammatic section through the carburetor of FIG. 2, but offset therefrom, and showing the idling circuit thereof; and

FIG. 4 is a diagrammatic side view of a load life vehicle of the invention.

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When using intake manifold depression to directly evacuate air through lifting attachments, changes are required in the carburetor because standard carburetors are designed for operation at atmospheric pressure less the small pressure drop caused by the air cleaner. In the following discussion, this pressure drop will be disregarded and the intake pressure of the carburetor will be referred to as atmospheric.

The present arrangement relies on the time-honored venturi pressure drop method of metering fuel but adds to this an automatic provision for adapting the carburetor to meter fuel to the engine under an exceedingly wide range of air intake pressures. Specifically, the subject carburetor will operate effectively either at atmospheric pressure or at intake pressure as low as 14 inches (mercury) absolute. Obviously, when the carburetor is operating at a low intake pressure, the engine does not produce as much power as when operating at atmospheric pressure because it cannot take in enough oxygen to burn sufficient fuel to produce the power. I find,- however, that the subject carburetor will give about 25% of full rotary power at a 15 inch mercury intake pressure, and will produce about 50% at 20 inches. This is far superior to the engine output of our previous systems and in addition to this, the current system is more reliable because it does not require delicate adjustment. The principal reason for the added efficiency is that the present carburetor will maintain a proper air/fuel ratio throughout its full operating range of intake pressures.

The standard automotive carburetor gives a fuel/air ratio of about 15 to 1 when operating at 'low engine loads. This is the ratio of maximum economy and hence gives the best gas mileage. The standard carburetor is equipped with an auxiliary jet known as the power, or economizer jet which acts to increase fuel/air ratio to about 12 to l for maximum engine power. The power jet comes into play automatically, as manifold vacuum is increased, by opening the throttle when the engine is incapable of speeding up because of torsional load. In a lift truck maximum fuel economy is not required since there is more interest in maximum power, so frequently my carburetors are adjusted to operate continuously without the power jet at a ratio between the extremes provided in the automotive carburetor, and aim at a fuel ratio of 14 .5 to 1 regardless of engine speed or 'load. However, the power jet can be used in my modified carburetor if desired. Subject device achieves a satisfactory fuel/air ratio so as to provide primary power for normal truck operation either at atmospheric intake pressure or when using the engine as a vacuum pump at intake pressures ranging from atmospheric to about 15 inches of mercury. Laboratory tests have proven that this goal has been attained.

OPERATION Standard carburetor under standard operation 'the throat of the main venturi 14. The reduced pressure through the venturi caused by the increased velocity is augmented by the boost venturi 6 and the resultant decrease in pressure at tends to lift liquid fuel up the discharge well 11 to the venturi level which has been designated diagrammatically at 7. Thus, the amount of fuel available at the venturi for mixture with air varies in proportion to the velocity of the air which in turn varies with the volume of air being drawn into the engine.

In a standard carburetor, air at air horn pressure is introduced into discharge well 11 at a level below liquid level. This is brought about by orifice 50, passage 51 and bleed hole 52. The purpose of introducing air at this point is to produce small bubbles which cause a turbulent flow of fuel up through well 11 and tend to reduce hydraulic friction. This effect is most noticeable and necessary at high engine speed and the bleeder is frequently referred to as the high speed bleeder. The bleeder is vented to air horn at 50 where the pressure is known as deck pressure and, for the purposes of the present discussion, will be considered atmospheric during normal operation. The vent which is shown at 9 is referred to as the impact tube and, as it projects out into the air stream, it is apparent that it will, by virtue of the impact of air, increase the pressure in the float chamber as air velocity through the horn increases tending to force fuel up the discharge well 11.

The standard carburetor is calibrated for various types of operation by the installation of a suitable fuel orifice 19 known as the main jet. The standard carburetor also provides various metering circuits to take care of power, economy and starting considerations. None of these circuits are shown in FIG. 1 because they do not enter into the present discussion and their operation is not affected by nor does it affect the modifications and additions about to be discussed.

FIG. 3 shows the idling circuit which has been modified in a manner to be described later. The standard carburetor prior to modifications includes a vent 60 shown in dotted lines as it would appear before modification. When the engine is idling, throttle 61 is almost completely closed so there is a very high vacuum below throttle 61 and atmospheric pressure above it. This difference in pressure causes a continuous flow of air through vent 6t), tube 62 and jet 63. The jet is normally adjustable with a needle valve which is not shown. It will be noted that there will be a high pressure in the float chamber above the fuel due to vent 9. This pressure will force fuel up idle well 64 to mix with the air flowing through tube 62. The amount of air permitted to flow through tube 62 and hence its static pressure is determined by the opening in orifice 63 which creates a resistance to the flow of air from the high pressure area above the throttle to the low pressure area below the throttle. During idling, there will be no flow of fuel through main jet because there is insufficient flow of air through the venturi to create the pressure drop necessary to draw fuel from well 11.

Standard carburetor under vacuumizing operation When the engine is to be used to evacuate air through a vacuum lifting device air horn 8 is connected to the vacuum device shown diagrammatically at 40. As soon as air is withdrawn from the vacuum device, the intake pressure of the carburetor is reduced from the normal inch mercury atmospheric pressure to 15 inches absolute for example. There are several effects of this, as follows:

(a) The air drawn into the engine is of low density having expanded to one-half atmosphere.

(b) The velocity of this air through the venturi is the same as under normal operation so, in spite of its reduced density, it still creates a metering differential pressure between air horn 8 and venturi throat at 6. This differential causes nearly as much fuel to flow through the jet as if the engine were under standard operation. a fuel/ air mixture so rich in fuel that it is hardly combustible.

(c) The low pressure at air horn 8 is transmitted through vent 9 to the float chamber which reduces the boiling point of fuel 3 in the float chamber. The temperature of the engine is so high that the fuel immediately begins to boil in the float chamber. Expanding fuel vapor forces additional fuel into the carburetor throat further enriching the mixture.

The result is (d) When relatively high pressure is maintained in the float chamber (which will be described later) to prevent boiling, it has the effect of forcing fuel up the discharge well 11 into the venturi 6 and also up idle well 64, into the carburetor main passage at the horn through vent 60, and also into the carburetor main passage below the throttle valve at jet 63. This is so because the entire carburetor barrel is at lower pressure than the fuel bowl. The result is an enriched mix which cannot be tolerated.

The effect of all this is that the engine will eventually stop running but during the borderline period, it may run so poorly that practically no rotary power can be taken from it and exhaust fumes become highly obnoxious. Therefore, it is not practical to use a standard carburetor when utilizing engine manifold depression to obtain air evacuation at flow rates comparable to intake air requirements of the engine even though the standard carburetor has for years permitted air evacuation at low flow rates as required by the conventional windshield wiper and other accessories.

FIG. 4 shows a typical self-powered load lift vehicle in which the carburetor system of the present invention is ideally incorporated. The vehicle shown is an industrial lift truck having a body B. An internal combustion engine E on the body drives traction wheels Wt, steerable wheels Ws being provided at the rear of the body. A mast M is provided on the front of the body B and guides a carriage C for vertical movement under the influence of a lifting device such as an hydraulic ram not shown. The carriage supports the suction device 40, which has a conduit 40:: extending therefrom to the carburetor system of the present invention. The carburetor system is indicated by the letters CS in FIG. 4.

Construction and operation of subject carburetor Referring to FIGS. 2 and 3, to overcome the condition described in (b) above, I provide a flow of air into the upper end of discharge well 11. This air increases the pressure at the upper end of the well and thus reduces the differential pressure which determines fuel flow. It is to be understood that the volume of air delivered here is so small that its direct effect on the fuel/ air ratio is negligible. Its only measurable effect is the regulation of the pressure differential across main jet 10. It is obvious that if enough air were introduced at this point, the flow of fuel could be stopped altogether, and if no air were introduced, an excess flow of fuel would obtain. In order to carry this out in an effective and controlled manner, the following additions and modifications are made to the carburetor:

(A) A. carefully calibrated discharge well nozzle restriction 12 is installed. In the standard carburetor no calibration is provided at this point so in order to get consistent and predictable results, I provide a critical orifice calibrated to have a specific effect on fuel flow.

(B) To effect this critical calibration, it is necessary to check the flow of air from the high speed bleeder 50 so a ball check 53 supported on a horizontal rod 54 is installed which will close orifice 50 when the pressure in passage 51 exceeds the :air horn pressure.

(C) The main jet 10 is slightly enlarged from standard to compensate for the restrictive effect of new orifice 12 and the tube about to be described.

(D) A controlled flow of air is introduced at the top of discharge well 11 by tube 13 or some other means. The control and modulation of the flow of air into the top of well 11 is brought about by calibrated orifice 24a which can be placed at the position shown in FIGURE 2.

In order to overcome boiling, as described in subparagraph (c) above, I provide a regulated flow into the float chamber of air at a pressure above deck pressure but less than ambient. This air is supplied and regulated by phasing valve 15 to be described later, and is delivered through tube 16. The flow of air through tube 16 is sufficient to maintain a pressure in the float chamber high enough to prevent boiling. As indicated earlier, vent In order to overcome the difficulty that would be experienced with the standard idling jet as described in paragraph (d), vent 61 is removed and a calibrated orifice is placed at 65 within the float chamber. During normal engine operation at idling speed, the float chamber pressure, being vented to the air horn through vent 9, is the same as the air horn pressure. Therefore, the idling circuit performs in a standard manner because there is a flow of air through tube 62 from the high pressure area in the float chamber to the low pressure area below throttle valve 61. During vacuumizing, throttle valve 61 is wide open but because I have pressurized the float chamber to something above air horn pressure, there will be a flow of air from orifice 65 through tube 62 and into the barrel through orifice 63. This air, however, will not pick up any substantial amount of fuel because the pressure at point 66 at the top of idle well 64 is not sufiicien-tly below the pressure on the fuel to cause the fuel to flow upfrom liquid level to point 66.

Construction and operation of phasing valve vacuum control As indicated above, device is called upon to supply air under precise and interrelated control to tubes 13 and 16, respectively. The main body of the device shown generally at 17 senses deck pressure through tube 18 which is connected to the air horn at 19. Pressure changes in air horn 21 are transmitted by tube 18 through check valve 20 (which will he described later) to the upper side of diaphragm 21. For reasons to be described later, I install a small orifice 27 in diaphragm 21 so there is a continuous, though exceedingly limited, flow of air through tube 18 in the direction of the carburetor, which maintains ball check 20 unseated so long as the air horn pressure, and thus the pressure in tube 18, is lower than the air pressure on the upper side of the diaphragm. In view of the fact that the flow through tube 28 to the lower side of the diaphragm is virtually unrestricted, there is a constant atmospheric pressure under the diaphragm in spite of the leakage through the diaphragm. Similarly, tube 18 can handle a much larger volume of .air than orifice 27, so the pressure above diaphragm 21 will be substantially equal to the deck pressure in spite of orifice 27. Thus, the differential across the diaphragm is not materially affected by the orifice. Attached to the center of the diaphragm is valvepoppet 22 which is urged by spring 23 to engage seat 24 when a certain predetermined, near atmospheric, carburetor air intake pressure is attained. The spring and the diaphragm are so calibrated that under normal intake pressure of about inches, no air passes into tube 13. When carburetor air intake pressure is reduced to a predetermined value, the pressure above diaphragm 21 is reduced, poppet 22 is raised from seat 24 and metered air is allowed to flow into tube 13 and tube 16. This provides a pressure balance which develops a float bowl pressure higher than intake air pressure (to prevent fuel boiling) without creating excessive pressure drop across the main fuel jet. Orifices 24a, 26 and 29 create circuit restrictions which cause a high percentage of the venturi metering pressure differential to appear across the main fuel jet, providing fuel metering with relation to intake air velocity. As intake air pressure varies, air flow through orifices 24a,

26 and 29 varies, altering the effect of venturi metering pressure differential thus providing fuel flow rates responding to changes in air density.

Delay valve the deck pressure almost instantly is raised from about 15 inch absolute pressure to ambient air at 30 inches. This would tend immediately to drop poppet 22 from seat 30 to seat 24 and shut off the supply of air to tube 13. At the same time, pressure in bowl 5 would be suddenly increased because of the rush of air through impact tube 9 r and an increased flow through tube 16. The effect of these two events would be to force an undue quantity of fuel into the throat of the carburetor which would cause the engine to falter. To prevent this, I install check valve 20 which will close under the sudden increase of carburetor intake air pressure. Thus, the pressure above diaphragm 21 will not increase until air can enter the chamber above the diaphragm through orifice 27 in the diaphragm. Orifice 27 is so small that it takes a perceptible amount of time for the pressure to build up above the diaphragm enough to close all the flow of air to tube 13. Thus, the flow of gasoline into the engine is not allowed to surge as it would otherwise do.

Float chamber pressure control The flow of air to tube 16 which maintains .a pressure in the float chamber high enough to prevent boiling, is regulated by orifice 29 which is calibrated in conjunction with the calibration of impact tube 9 and orifices 26 and 24a. During normal operation, poppet 22 will be in down position so ambient air will be free to flow through tube 28, seat 30, orifice 29 and tube 16 into the float chamber. Normally, it would be expected that this flow of air would effectively maintain float chamber pressure at atmospheric. This wouldbe so if it were not for the fact that air is constantly flowing out of the float chamber through impact tube 9 because the deck pressure is slightly less than atmospheric due to loss through the air filter which is normally attached to the carburetor intake. By calibrating both impact tube 9 and orifice 29, I can effectively control, float chamber pressure at a value slightly less than atmospheric so as to approach the normal calibration of the carburetor.

When the engine is used for vacuumizing, a low pressure is maintained above diaphragm 21, as discussed above, so poppet 22 engages seat 30 with the result that the only air available to tube 16 is that which enters through orifice 26 and tube 25. This air is divided between a flow through tube 13 as previously discussed and a flow through tube 16. Obviously, there will be less flow through tube 16 under these conditions than under the normal operating condition where unlimited air is available at orifice 29 through tube 28. It will-be remembered that during the vacuumizing cycle the pressure at the air horn is relatively low so the flowof air out of the float chamber through vent 9 will be increased. This,

in conjunction with a reduced flow into the chamber through tube 16, will reduce the float chamber pressure. The calibration of orifices 26 and 29, and of vent 9 are such that the pressure in the float chamber can never get below a value of about 21 inches absolute. This pressure is enough to prevent boiling of the fuel under the temperature conditions experienced. It will be seen that as carburetor intake velocity, or pressure, or both vary, interactions of restrictions 26, 29, 24a, 9, 10' and 12 combine with carburetor metering pressure differentials to prdouce modulated metering pressure differentials which 0 automatically provide the proper fuel delivery rate required while maintaining float bowl pressure above fuel vapor pressure.

In summary, the present invention provides:

(A) Modifications to a standard carburetor which will permit it .to maintain a relatively constant fuel/air ratio throughout an abnormally wide range of deck pressure.

(B) Control of the fuel/air ratio automatically by introduction of a modulated flow of air between the main jet and the venturi, working in cooperation with a modulated control of float chamber pressure.

(C) Controlled pressure in the float chamber at a value high enough to prevent boiling at elevated underhood temperatures in spite of a vacuumizing deck pressure below this value.

(D) Modifications in the idling circuit to automatically compensate for drastic reduction in deck pressure.

(E) A carburetor which is simple to manufacture, positive, tamper-proof and inexpensive. It contains only one moving part (a simple non-adjustable shuttle valve).

It is pointed out that reference to ambient air is made in the specification and claims, and to the supply of ambient air to the upper end of the well 11. It will be appreciated that such ambient air will normally be routed through an air filter, to reduce its pressure somewhat, and its further routing through various ducts, conduits and passages will further reduce its pressure. However, the pressure available at the upper end of the discharge well, will still exceed that in the main passage or barrel of the carburetor.

The various orifices, ducts and passages of the carburetor system will be calibrated in the usual manner employed by carburetor manufacturers, and it is apparent that the sizes of such orifices, etc., will vary with engine capacity and other factors.

The present invention has provided a carburetor system in which the basic venturi action of the carburetor is left intact for ordinary operation of the engine, but is suppressed somewhat whenever the pressure in the system drops, whereby to obtain a proper air-fuel ratio under both normal and low intake air pressures. By suppressed it is meant that the range of the operation of the veturi is shifted, so that it causes the delivery of less fuel than otherwise would be the case, but is still responsive to velocity changes to cause variations in fuel delivery. This suppressing or depressing effect is achieved 'by supplying higher pressure ambient air to the upper end of the discharge well of the carburetor, and providing an orifice 12 at the discharge end of such well so that the egress of air from such well into the venturi is restricted whereby the level of the pressure in the upper end of the discharge well is raised. This reduces the diffedential pressure between the float chamber and the upper end of the well, and thus the supply of fuel hereinbefore stated. However, the raising of the pressure level in the upper end of the well is in the nature of a superimposed control, which does not interfere with variations in such differential pressure as are caused by changes in the velocity of the air through the venturi 6. This is explained by the fact that the auxiliary control which comes into play when the engine is used as a vacuum pump is essentially responsive to changes in the density (pressure) of the air in the system, while the venturi is responsive to the velocity of the air passing through the veturi 6. It follows that for a given air density or pressure in the system, the fuel supply is regulated by changes in the velocity of the air through the venturi. Also, for a given velocity of the air through the venturi; the fuel supply is regulated by changes in the density (or pressure) of the air in the system. When there are changes in both density of the air in the system and the velocity of the air through the venturi, as frequently occurs, the fuel is regulated by the mutual interaction of such changing conditions.

In order for the auxiliary control to exert only a superimposing effect on the control exercised by the venturi 6, the flow of air to the upper end of the discharge well must be controlled. If unlimited air were available, the air delivered by the tube 13 would cancel out or severely interfere with the control exercised by the venturi 6.

The proper supply of air to the upper end of the well is primarily controlled by the orifice 24a. This orifice is of such size that it restricts the supply of air to the upper end of the well through the tube 13 so that the resulting pressure does not cancel out the control exercised by the venturi but only depresses it.

It is pointed out that if the anti-boiling control arrangement were eliminated, such as might be the case with an engine to be used only in a cool environment, the line 16 and its orifice 29, line 28, and the orifice 26 in line 25 could be eliminated. It would still be necessary to employ the valve 22, because without the valve, air would be supplied to the well during ordinary engine operation. This would cause a lower amount of fuel to be delivered by the well than required.

It is apparent from what has been stated above that obtaining maximum rotary or flywheel power is of the greatest importance during ordinary or normal engine operation, but that obtaining maximum power at the inhake is of greatest importance when the engine is used as a vacuum pump. This is obtained in the present invention by modifying in a simple fashion an existing commercial carburetor.

I have provided a simple compensating device for automotive type carburetors, which responds automatically to variation in engine intake air pressure to establish correct air-fuel mixtures during normal engine aspiration, as well as when an intake air pressure drop is created to obtain substantial power from the engine in the form of intake air to ambient air pressure differential at high air flow rates. In one engine built according to my concepts, the response to variation was between 30 inches Hg to 15 inches Hg absolute; the fuel/air ratio was maintained within the range of 13 to 15:1; the power obtained from the engine when acting as a pump was in the order of 1-5% of the engines rated rotational horsepower with 50 to 25% of rotational horsepower also available as primary power for the truck; and the flow rates were on the order of 40% of engine displacement at 2000 rpm.

Having described the invention in what is believed to be the preferred embodiment thereof, it is desired that it be understood that the invention is not to be limited other than by the provisions of the following claims.

I claim:

1. A carburetor system for the internal combustion engine of a self-powered load lifting vehicle of the type in which the engine serves to drive the traction wheels of the vehicle, and in which the engine at times functions as a vacuum pump for a suction type load lifting mean said carburetor system comprising: 1

a carburetor for operation at low intake pressure,

a float chamber with liquid fuel therein with a vent to said intake pressure,

and means including an auxiliary air inlet and calibrated fixed orifice means providing a controlled flow of air into said chamber and out said vent at a velocity which varies in response to variations in intake pressure, such that under low intake pressures said float chamber is maintained at a pressure higher than said intake pressure to prevent boiling of said fuel, and such that the flow of air out said vent in no event is sufficient to cause any appreciable increase in intake air pressure,

and valve means responsive to said intake pressure to modulate said controlled flow of air.

2. A carburetor system for the internal combustion engine of a self-powered load lifting vehicle of the type in which the engine serves to drive the traction wheels of the vehicle, and in which the engine at times functions as a vacuum pump for a suction type load lifting means, said carburetor system comprising:

a carburetor having a main passage including an inlet end, a venturi in said main passage, a float chamber, and a discharge well leading upwardly from said float chamber to said main passage,

dilferential pressure means responsive to the difference in pressure between that in the inlet end of said carburetor and to a pressure close to that of the ambient air to supply ambient air to theupper end of said well, when said engine is functioning as a vacuum pump, to decrease the effective differential pressure created by said venturi and accordingly decrease the fiow of fuel into said venturi,

means responsive to a sudden increase in pressure in the inlet end of said carburetor to temporarily isolate said differential means from the pressure in such inlet end.

3. A carburetor system for the internal combustion engine of a self-powered load lifting vehicle of the type in which the engine serves to drive the traction wheels of the vehicle, and in which the engine at times functions as a vacuum pump for a suction type load lifting means, said carburetor system comprising:

a carburetor having a main passage including an inlet end, a venturi in said main passage, a float chamber, and a discharge well leading upwardly from said float chamber to said main passage,

differential pressure means responsive to the difference in pressure between that in the inlet end of said carburetor and to a pressure close to that of the ambient air to supply ambient air to the upper end of said Well, when said engine is functioning as a vacuum pump, to decrease the effective differential pressure created by said venturi and accordingly decrease the flow of fuel into said venturi,

duct means exposed to the air passing through the main passage of said carburetor for directing a portion of such air to said discharge well below the level of the fluid therein,

and means operable in response to a drop in the pressure of the air in the inlet end of said main passage for closing said duct means.

4. In a vehicle for lifting loads having an internal combustion engine, a venturi-type carburetor for mixing air with fuel to provide a combustible mixture for said engine wherein the differential pressure created by the venturi of the carburetor is effective to control the supply of fuel, said carburetor including a fuel discharge Well having an upper end opening into said venturi, means providing a regular air inlet for communication of said carburetor with the ambient air, a suction-type load pickup device, and means for terminating the flow of ambient air from said regular air inlet to said carburetor and connecting said device to said carburetor so that substantially the entire supply of intake air for the engine comes from said device whereby a subatmospheric pressure can be created at said device when said device is against a load,

the improvement comprising:

a regulating means for controlling the fuel-to-air ratio of said carburetor in a manner to maintain a substantially optimum ratio despite changes in the pressure of the intake air so that said engine operates properly at both normal and reduced air intake pressures,

said regulating means including an auxiliary ambient air inlet means,

passage means connecting said auxiliary inlet means to the upper end of said discharge well above the fuel .level therein,

and responsive means operable in response to a predetermined drop in the intake air pressure of said carburetor to supply ambient air to the upper end of said discharge well from said auxiliary air inlet in such quantities and in such a manner as to cause said differential pressure to assume a value less than it would otherwise have to accordingly lessen the supply of fuel to said engine, all without substantially raising the pressure of the intake air,

said responsive means including valve means for controlling the flow of ambient air to said discharge well from said auxiliary air inlet,

and valve-actuating means including intake air pressure sensing means operable to close said valve means to prevent the flow of ambient air to said discharge well from said auxiliary air inlet under normal intake air pressures and operable to open said valve means to permit the flow of ambient air to said discharge well under substantially reduced intake air pressures.

5. In a vehicle for lifting loads having an internal combustion engine, a venturi-type carburetor for mixing air with fuel to provide a combustible mixture for said engine wherein the differential pressure created by the venturi of the carburetor is effective to control the supply of fuel, said carburetor including a fuel discharge well having an upper end opening into said venturi, means providing a regular air inlet providing for communication of said carburetor with the ambient air, a suctiontype load pickup device, and means for terminating the flow of ambient air from said regular air inlet to said carburetor and connecting said device to said carburetor so that substantially the entire supply of intake air for the engine comes from said device whereby a subatmospheric pressure can be created at said device when said device is against a load,

the improvement comprising:

a regulating means for controlling the fuel-to-air ratio of said carburetor in a manner to maintain a substantially optimum ratio despite changes in the pressure of the intake air so that said engine operates properly at both normal and reduced air intake pressure,

said regulating means including an auxiliary ambient'air inlet means,

passage means connecting said auxiliary inlet means to the upper end of said discharge well above the fuel level therein,

and responsive means operable in response to a predetermined drop in the intake air pressure of said carburetor to supply ambient air to the upper end of said discharge well from said auxiliary air inlet in such quantities and in such a manner as to cause said differential pressure to assume a value less than it would otherwise have to accordingly lessen the supply of fuel to said engine, all without substantially raising the pressure of the intake air,

said responsive means including valve means for controlling the flow of ambient air to said discharge well from said auxiliary air inlet,

and valve-actuating means including intake air pressure sensing means operable to close said valve means to prevent the flow of ambient air to said discharge Well from said auxiliary air inlet under normal intake air pressure and operable to open said valve means to permit the flow of ambient air to said discharge well under substantially reduced intake air pressures,

said passage means including a calibrated orifice to regulate the ambient air flow into said discharge well when said valve is open.

6. A carburetor system for the internal combustion engine of a self-powered load-lifting vehicle of the type in which the engine serves to drive the traction wheels of the vehicle, and in which the engine at times functions as a vacuum pump for a suction-type load-lifting means, i

said carburetor system comprising:

a carburetor adapted to operate alternately under a low intake air pressure and under a normal intake air pressure,

a venturi in said carburetor having a throat with a throat pressure less than said intake pressure, a calibrated fuel entrance orifice at the throat of said venturi, a float chamber including a float and float valve means maintaining a fuel level in said chamber, a fuel discharge well leading upwardly from said float chamber to said fuel discharge orifice, a calibrated fuel-metering orifice connecting said chamber and said well below said fuel level, and means for supplying air at a pressure higher than said throat pressure between said fuelmetering orifice and said fuel entrance orifice at a point above said liquid level in said well, said air serving to control the flow of fuel into said venturi,

said means including ambient air passage means and calibrated air metering orifice means in said passage means,

said fuel-metering orifice, said fuel entrance orifice, and said air-metering orifice being mutually calibrated such that a back air pressure is created between said fuel level in said well and said fuel entrance orifice to retard the flow :of fuel into said throat at low intake air pressure, and such that the effective differential air pressure across said fuel-metering Orifice is decreased upon a decrease in intake air pressure and increased upon an increase in intake air pressure so as to maintain a substantially constant fuel-air ratio irrespective of carburetor intake air pressure.

7. In a carburetor subject to occasional intake pressures substantially less than atmospheric pressure,

a fuel bowl including means maintaining a liquid level in said bowl,

a venturi with a throat above said liquid level,

' means defining a first passage leading from said bowl to said throat,

means defining a fuel orifice below said liquid level connecting said bowl and said first passage,

means for modulating fuel flow through said fuel orifice embodying the introduction of a modulated flow of air into said passage so as to create a pressure balance in said passage that will retard the flow of fuel proportionately as said intake pressure is reduced,

an idling circuit including a Well leading upwardly from said first passage to a point above said liquid level,

first orifice means below said liquid level within said first passage and opening into said well,

means defining a second passage leading downwardly from said .point into said venturi below said throat,

a second orifice means connecting said second passage to said venturi below said throat,

and third orifice means within said bowl above said liquid level placing the interior of said well in communication with the interior of said bowl.

8. In a carburetor subject to occasional intake pressures substantially less than atmospheric pressure,

a fuel bowl including means maintaining a liquid level in said bowl,

a venturi with a throat above said liquid level,

means defining a first passage leading from said bowl to said throat,

means defining a fuel orifice below said liquid level connecting said bowl and said passage,

means for modulating fuel flow through said orifice embodying the introduction of a modulated flow of air into said passage so as to create a pressure balance in said passage that will retard the flow of fuel proportionately as said intake pressure is reduced,

an idling circuit including a well leading upwardly from said first passage to a point above said liquid level,

first orifice means below said liquid level within said first passage and opening into said well,

means defining a second passage leading downwardly from said point into said venturi below said throat, a second orifice means connecting said second passage to said venturi below said-throat,

and third orifice means within said bow-l above said liquid level placing the interior of said well in communication with the interior of said bowl,

said first, second and third orifice means being mutually calibrated such that the flow of fuel through said second orifice is substantially eliminated when the carburetor intake pressure is substantially below atmospheric pressure.

9. In a carburetor subject to normal atmospheric intake pressures and abnormally low intake pressures substantially less than atmospheric pressure,

a float chamber including means maintaining a liquid level in said chamber,

a fuel discharge passage leading from said chamber to a discharge orifice, venturi means in communication with said orifice and operable under normal intake pressures for increasing the discharge of fuel into said venturi in response to a velocity increase in said venturi means,

and overriding control means operable under abnormally low intake pressures to override the normal action of said venturi means by supplying a modulated flow of air to said passage suflicient to create a back pressure therein and thereby reduce the amount of fuel discharged in response to decreases in intake pressures.

10. The method of regulating the air-to-fuel ratio of the combustible mixture in a carburetor subjected to wide variations in intake air pressures including a first normal range extending between substantially ambient intake air pressure and a lower pressure, and a second abnormally low range including intake air pressures below said lowe-rpressure and substantially below ambient pressure, said carburetor including a fuel bowl, a main passage, a venturi'in said main passage including a throat, and a fuel discharge well leading upwardly from said bowl and having a discharge orifice opening into said throat, I

said method comp-rising the steps:

supplying ambient air to the upper end of said well whenever the air pressure in the main passage drops into the abnormally low pressure range,

and while said intake pressure is in said abnormally low range, modulating the flow of ambient air into said well such that a back pressure is created at the upper end of said well suflicient to retard the flow of fuel into said throat without stopping the same and such that the flow. of fuel into said throat remains responsive to velocity changes in said throat,

lfurther modulating said flow to decrease the effective differential pressure acting on the fuel in said chamber upon decreases in intake pressure in said abnormal-1y low pressure range,

and shutting off said flow of ambient air whenever the intake air pressure returns to said normal range such that drops in intake pressures within said normal range have substantially no effect on the operation of said venturi.

1 1. A carburetor as claimed in claim 9 including valve means responsive to changes in intake air pressures for stopping said modulated flow of air when said intake pressure returns substantially to atmospheric pressure and to permit said modulated flow when said intake pressure drops substantially below atmospheric pressure.

(References on following page) References Citei by the Examiner 3,110,517 11/1963 O1s3n et 21.

UNITED STATES PATENTS 3,187,989 6/1965 2/1964 Cushmn GERALD M. EOR-LENZA, Primary Examiner. 311323 56233325533313: $1 32??? 5 MORRIS TEMIN, 10/1959 Goetz 261-72 X R. B. JOHNSON, Assistant Examiner. 

9. IN A CARBURETOR SUBJECT TO NORMAL ATMOSPHERIC INTAKE PRESSURE AND ABNORMALLY LOW INTAKE PRESSURES SUBSTANTIALLY LESS THAN ATMOSPHERIC PRESSURE, A FLOAT CHAMBER INCLUDING MEANS MAINTAINING A LIQUID LEVEL IN SAID CHAMBER, A FUEL DISCHARGE PASSAGE LEADING FROM SAID CHAMBER TO A DISCHARGE ORIFICE, VENTURI MEANS IN COMMUNICATION WITH SAID ORIFICE AND OPERABLE UNDER NORMAL INTAKE PRESSURES FOR INCREASING THE DISCHARGE OF FUEL INTO SAID VENTURI IN RESPONSE TO A VELOCITY INCREASE IN SAID VENTURI MEANS, AND OVERRIDING CONTROL MEANS OPERABLE UNDER ABNORMALLY LOW INTAKE PRESSURES TO OVERRIDE THE NORMAL ACTION OF SAID VENTURI MEANS BY SUPPLYING A MODULATED FLOW OF AIR TO SAID PASSAGE SUFFICIENT TO CREATE A BACK PRESSURE THEREIN AND THEREBY REDUCE THE AMOUNT OF FUEL DISCHARGED IN RESPONSE TO DECREASES IN INTAKE PRESSURES. 